[gst-devel] AppSink vs FileSink question

[thiagossantos at gmail.com]

On Sun, Jul 4, 2010 at 11:42 AM, Andrey Nechypurenko <
andreynech at googlemail.com> wrote:

> Hi Folks,
>
> In my application I want to capture the output of the encoding
> pipeline for further processing. So my assumption was that using
> appsink would give me the same byte stream as the one stored in file
> with filesink. To be more concrete, I have the following pipeline:
>
>  pipeline =
>    GST_PIPELINE(gst_parse_launch
>                 ("videotestsrc ! "
>                  "video/x-raw-yuv,width=640,height=480,framerate=30/1 ! "
>                  "x264enc ! "
>                  "matroskamux ! "
>                  "appsink name=mysink",
>                  NULL));
>
> then, after setting up the callback I just write the buffer into file:
>
>  GstElement *mysink = gst_bin_get_by_name(GST_BIN(this->pipeline),
> "mysink");
>  g_object_set(G_OBJECT(mysink), "emit-signals", TRUE, "sync", FALSE, NULL);
>  g_signal_connect(mysink, "new-buffer", G_CALLBACK (on_new_buffer), NULL);
>
> static void
> on_new_buffer(GstElement *element, void *data)
> {
>  GstBuffer *buffer = gst_app_sink_pull_buffer(GST_APP_SINK(element));
>  fwrite(GST_BUFFER_DATA(buffer), GST_BUFFER_SIZE(buffer), 1, f);
>  gst_buffer_unref(buffer);
> }
>
> To my surprise, the content of the file is not recognized as matroska
> container. The header (the beginning of the file) is indeed totally
> different from what I get if I execute the following command line:
>
> gst-launch videotestsrc !
> video/x-raw-yuv,width=640,height=480,framerate=30/1 ! x264enc !
> matroskamux ! filesink location=test.mka
>
> So my question is - am I right assuming that my application with
> appsink should produce correct mka file similar to the command line
> with filesink?
>

The problem here is that muxers usually have to seek back to rewrite some
values it didn't know from the start to properly finish the file. Appsink
doesn't provide a way to notify about this and filesink obviously handles
it.

Checkout this bug for further info:
https://bugzilla.gnome.org/show_bug.cgi?id=570619


>
> If not, I would appreciate any suggestion or hints on how the pipeline
> should looks like to playback what is recorded by appsink in the
> scenario mentioned above.
>
>
> Thank you very much!
> Andrey.
>
>
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-- 
Thiago Sousa Santos
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